Requests for adhesives that cure in a short period of time at ambient temperature have steadily increased due to the desire for greater production line efficiency and lower costs. Conventionally, those well-known as adhesives of a quick curing type at ambient temperature include two-part quick curing type epoxy adhesives, instant adhesives, anaerobic adhesives, non-anaerobic acryl adhesives and the like.
The two-part quick curing type epoxy adhesive is one used by weighing and mixing a base compound and a curing agent. If they are insufficiently weighed and mixed, a remarkable reduction in strength is likely. Also, even if they are sufficiently weighed and mixed, there is a drawback that peeling strength and impact strength are low.
Such an adhesive has excellent workability, but is generally low in peeling strength and impact strength, and is inferior in heat resistance and moisture resistance. Thus, the range of its use is remarkably limited.
The anaerobic adhesive is cured by pressure-bonding the adhesive between materials to be adhered to block air. Thus, as a matter of course, a portion in contact with air, such as a portion protruding from between adherends is not cured. Therefore, when the adherend is porous or shapes of the adherends between the adherends are different, an adhesion thickness is partially different, i.e., degrees of the adherends in contact with air are different. Thus, it is difficult to cure the adhesive anaerobically.
The non-anaerobic acrylic adhesive is generally referred to as a second generation acrylic adhesive (SGA), and is a two-part agent. The non-anaerobic acrylic adhesive has excellent workability in that accurate weighing of two preparations is not required and the adhesive is cured in several to several tens of minutes at ambient temperature even if the preparations are extremely roughly weighed and mixed, and has high peeling strength and impact strength. The portion protruding from between the adherends is also cured well. Thus, this is widely used.
However, requests to further shorten curing time for acrylic adhesives that require several to several tens of minutes for curing at ambient temperature have been increasing due to the desire for greater production efficiency and lower costs.
For example, the adhesive disclosed in Patent Document 1 is composed of urethane acrylate, an acrylate ester monomer, aromatic perester, an organic acid and a transition metal, and cures in 45 seconds.
Also, the adhesive disclosed in Patent Document 2 is composed of certain urethane acrylate, an acrylate ester monomer, peroxy ester and an accelerator, and cures within one minute.
It has been disclosed that the adhesive disclosed in Patent Document 3 contains chloro-sulfonated polyethylene and a particular acrylic monomer mixed at a particular ratio, further contains cumene hydroperoxide, an aldehyde-amine condensate and an oxidizing organic compound of a transition metal, and cures within several seconds.
Quick curing acrylic adhesives containing an acrylic monomer, a reaction condensate of peroxy ester and amine-aldehyde, a salt of copper and an aromatic hydroxyl group-containing compound are disclosed in Patent Documents 4 and 5. A curable composition containing a polymerizable acrylic liquid composition, cumene hydroperoxide, a reducing agent and a basic compound is disclosed in Patent Document 6.